Apparatus and method for forming a support column in soil

ABSTRACT

The present invention provides a method of forming a support column in soil using a reverse circulation down-the-hole hammer apparatus. The method includes drilling a hole with a reverse circulation down-the-hole hammer apparatus having a drill string with a return outlet and a down-the-hole hammer, and forming a column of mortar-like substance by pumping a mortar-like substance down the return outlet while lifting the apparatus out of the hole.

FIELD OF INVENTION

[0001] The present invention relates to an apparatus and method for forming support columns in soil. In particular, the present method utilizes a down-the-hole hammer to form support columns in soil.

BACKGROUND OF THE INVENTION

[0002] Support columns have typically been formed in soil by the following two methods. In the first method, a hole is first formed with a drilling apparatus, and then filled with a drill slurry, typically after drilling is completed but before removal of the drilling apparatus, to prevent cave in of the hole. The drill slurry is typically a mixture of clay (e.g., bentonite or a synthetic alternative) and water. A large diameter tremie pipe, typically a 6-inch diameter steel pipe, is then inserted into the hole filled with the drill slurry. A mortar-like substance, such as grout or concrete, is then pumping into the inner diameter of the tremie pipe to displace the drill slurry. Then the tremie pipe is removed before the grout or concrete hardens. A steel structure can also be installed into the plastic grout or concrete (e.g., before hardening) in order to provide added rigidity and reinforcement. This method is time consuming and messy. It takes a considerable amount of time to sequentially conduct each of the above steps. As the grout or concrete displaces the drill slurry in the hole, the drill slurry is forced to the surface of the ground and typically spreads around the work site, thereby requiring a substantial amount of time and expense for cleaning up the work site.

[0003] Alternatively, the second method typically includes forming a hole with a drilling apparatus and utilizing a pipe casing behind the drilling apparatus. Pile casings are typically used when drilling is conducted in soil that is likely to result in cave in of the hole. The pipe casing is typically about the same diameter as the drilling apparatus, and is not attached to the drilling apparatus. Accordingly, as the drilling apparatus advances into the hole, the pipe casing is separately forced into the hole, e.g., hammered or driven, to continue the advance of the pipe casing behind the drilling apparatus down the formed hole. When a desired depth of the hole is achieved, the drilling apparatus is removed through the pipe casing. Metal structures can be installed in the pipe or casing for reinforcement, and a tremie pipe is then inserted into the pipe casing to pump the mortar-like substance, such as grout or concrete, into the pipe casing. The casing is then removed before the grout or concrete hardens. This method is also time consuming to sequentially conduct each of the above steps, and it requires additional equipment and materials to advance and remove the pipe casing. Furthermore, care must be taken during removal of the pipe casing to prevent dislodgment of the reinforcing metal.

[0004] In order to address these disadvantages, some drilling apparatuses are made with dedicated internal lines for pumping grout. This configuration allows forming grout support columns without the need for drilling slurry. Such drilling apparatuses, however, result in increased costs in material and manufacturing to form the dedicated lines. In addition, the diameter of the dedicated grout lines are limited due to space considerations in the drill string of a reverse circulation down-the-hole hammer apparatus, which require at a minimum an exterior annulus for injecting the drilling fluid (e.g., air or water) to activate the hammer and a central passageway or bore for evacuating the cuttings, debris, and drilling fluid. The limited diameters of the grout lines do not allow the use of these lines for more coarse support materials, such as concrete, which is typically a mixture of cement, aggregates, and water. Such drilling apparatus are also disadvantages, because the dedicated grout lines can only be extended as far down as the back head assembly of the reverse circulation hammer. There simply is no room for the dedicated grout lines closer to the drill bit. Accordingly, the grout is pumped out around the back head assembly, thereby covering the outer covering of the hammer and drill bit with the grout. Expelling the grout around the back head assembly can also result in an unwanted increase in diameter of the drilled hole. These drilling apparatuses also require some over drilling, e.g., beyond a desired depth, because the tip of the drilling apparatus is below the grout exit ports.

[0005] There is, therefore, a need to develop a method of forming a support column in soil that addresses these disadvantages.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method for forming a support column in soil using a reverse circulation down-the-hole apparatus. The method includes drilling a hole with a reverse circulation down-the-hole hammer apparatus having a down-the-hole hammer connected to a drill string with a return outlet, and forming a column of mortar-like substance by pumping a mortar-like substance down the return outlet while lifting the apparatus out of the hole. It is preferred to lift the apparatus out of the hole at a vertical rate that is substantially equivalent to the vertical fill rate of the mortar-like substance into the portion of the hole evacuated by the apparatus. The method can further include the step of installing a metal reinforcing structure into the hole filled with the mortar-like substance before it hardens.

[0007] The present invention also provides a preferred apparatus that can be used to practice the method described above. The apparatus includes: a down-the-hole hammer having a back end and a drill bit end; a drill string having an inner passageway, one end of the drill string connected to the back end of the down-the-hole hammer and the other end of the drill string connected to a cuttings discharge swivel; and a mortar-like substance intake valve attached to the cuttings discharge swivel. The apparatus can further include a pipe casing connected to the down-the-hole hammer, thereby enveloping the drill string. In one embodiment, the pipe casing is connected to the back of the down-the-hole hammer. In another embodiment, the pipe casing is connected to and envelops at least a portion of the down-the-hole hammer. In still another embodiment, the pipe casing can be connected to the drill bit, thereby enveloping the down-the-hammer and drill string.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter, which is regarded as defining the present invention, it is believed that the invention will be better understood from the following description taken in conjunction with the following accompanying drawings:

[0009]FIG. 1 is a side view of a reverse circulation down-the-hole hammer during drilling; and

[0010]FIG. 2 is a side view of a reverse circulation down-the-hole hammer during support column formation.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention provides a novel method of utilizing a reverse circulation down-the-hole hammer apparatus (“DTH apparatus”) to form a support column of a mortar-like substance in soil. The method includes drilling a hole to a desired depth with the reverse circulation DTH apparatus having a drill string with a return outlet and a down-the-hole hammer, and pumping a mortar-like substance down the return outlet while lifting the apparatus out of the hole to form a column of the mortar-like substance. The term “return outlet,” as used herein, means a central bore or a passageway defined through a drill string, a drill piston and a bit, through which drilling fluid, cuttings and debris are exhausted to the surface. The term “mortar-like substance,” as used herein, means a plastic building material that is initially fluid enough to be pumped but hardens or sets. Nonlimiting examples of mortar-like substances include grout (e.g., including a mixture of at least cement and water), mortar (e.g., including a mixture of at least cement, sand, and water), concrete (e.g., including a mixture of at least mixture of cement, aggregates and water) and mixtures thereof. An aggregate is known in the art as a combination of different sized rock.

[0012] As illustrated in FIG. 1, the present method includes drilling a hole in the ground 65 to a predetermined depth, which can be below the ground water table 70, with a reverse circulation DTH apparatus 5. Reverse circulation DTH apparatuses are well known in the art, and any of the known reverse circulation DTH apparatuses can be used in the present method. Examples of suitable reverse circulation drilling apparatuses include, but are not limited to, U.S. Pat. No. 4,819,746 titled “Reverse circulation down-the-hole hammer drill and bit therefor,” U.S. Pat. No. 4,921,052 titled “Downhole recirculating hammer,” U.S. Pat. No. U.S. Pat. No. 5,685,380 titled “Reverse circulation down-the-hole drill,” U.S. Pat. No. RE36,002 titled “Transmission sleeve for a down hole hammer,” U.S. Pat. No. 5,957,226 titled “Reverse circulation drilling system with hexagonal pipe coupling,” and U.S. Pat. No. 5,975,222 titled “Reverse circulation drilling system with bit locked underreamer arms,” which are all incorporated herein by reference in their entireties.

[0013] As illustrated in FIG. 1, reverse circulation DTH apparatuses typically include a drill string 37 connected to a down-the-hole hammer 20 at one end of the drill string (i.e., at the back end which is opposite the drill bit end) and a cuttings discharge swivel 45 at the other end of the drill string. The down-the-hole hammer includes a main body, a piston (not shown), and an anvil (not shown). Since the drill string is a double-walled pipe that channels fluids from the surface to the down-the-hole hammer while returning cuttings to the surface, the drill string and the down-the-hole hammer are typically purchased from the same manufacturer to insure that the drill string conforms with the requirements of the down-the-hole hammer. The drill string typically includes an exterior annulus 35, which is connected near the top to a drilling fluid intake swivel connected to a hose 30, and an interior central bore or passageway 40 defined through the drill string, which communicates with a passageway in the drill piston and drill bit 25 for evacuating cuttings, debris, and used drilling fluid. The drilling fluid (e.g., compressed gas such as air, liquid such as water or oil, or a mixture of gas and liquid) is typically circulated via hose 30 down the exterior annular space 35 inside the drill string. The drilling fluid can be supplied to a piston within a chamber (not shown) in the down-the-hole hammer 20, so as to drive the piston forwardly towards a drill bit 25 mounted for sliding movement in a chuck (not shown) at the forward end of the down-the-hole hammer 20, to strike the bit 25 at the end of its downward stroke, and then to lift the piston in the opposite direction within the chamber, whereupon the cycle is repeated. Drilling fluid, cuttings and debris are removed through the return outlet 40 and exhausted to the surface via cuttings discharge swivel 45 and discharge hose 50. After reaching a predetermined depth, drilling is stopped, and the remaining cuttings/debris are preferably removed from the return outlet using the drilling fluid without advancing the DTH apparatus further into the ground.

[0014] A pipe casing 15, typically having a diameter about equal to the diameter of the down-the-hole hammer, can be placed behind the back end of the down-the-hole hammer, thereby enveloping the drill string 37 and preventing any cave in of the hole. Such a pipe casing is attached to the down-the-hole hammer and is typically driven or hammered separately into the ground for advancement behind the down-the-hole hammer.

[0015] The present method also includes forming a column of mortar-like substance 75 by pumping the mortar-like substance down the return outlet 40 while lifting the reverse circulation down-the-hole hammer apparatus 5 out of the drilled hole, as illustrated in FIG. 2. Since the pipe casing 15 has about the same diameter as the down-the-hole hammer, the pipe casing is lifted out of the hole along with the DTH apparatus. This method utilizes the return outlet 40 of the drill string 37 as a tremie pipe to pump the mortar-like substance into the hole. The mortar-like substance is pumped in at a rate and pressure typically known to the skilled artisan for use in tremie pipes. One method to attach the DTH apparatus (e.g., the drill string attached to the down-the-hole hammer) to a drill rig is to utilize a top drive 10 near one end of the DTH apparatus. Drilling rigs for holding, lowering, and raising DTH apparatuses are well known in the art. For example, drill rigs are commercially available from Champion Equipment Company located in Paramount, Calif. and from Soilmec located in Cesena, Italy. Accordingly, it is well known to the skilled artisan to adapt drilling rigs to include features for controlling the rate of raising a DTH apparatus. In this step, it is preferable to start raising or lifting the DTH apparatus out of the drilled hole just after, preferably about 5 to 30 seconds after, more preferably about 10 to 20 seconds after, initiating the pumping of the mortar-like substance, thereby minimizing the likelihood of a cave in of the drilled hole. Lifting of the DTH apparatus is more preferably commenced after the mortar-like substance substantially fills the entire volume of the return outlet 40 and the face of the drill bit. The DTH apparatus is most preferably raised or lifted at a vertical rate that is substantially equivalent to the vertical fill rate of the mortar-like substance into the portion of the hole evacuated by the hammer.

[0016] In order to conduct this column formation step of the method, known or commercially available reverse circulation DTH apparatuses can be modified to include a component that allows the mortar-like substance to be pumped into the return outlet. This can be achieved, for example, by detaching the cuttings/debris discharge hose 50 from the cuttings discharge swivel 45 and replacing it with an intake hose (not shown) for the mortar-like substance. Alternatively, a mortar-like substance intake valve 53 can be inserted in between the cuttings discharge swivel 45, which communicates with the return outlet 40, and the cuttings/debris discharge hose 50, as illustrated in FIGS. 1 and 2, to allow drilling and pumping operations without removal of hoses. The intake valve 53 includes a body portion in fluid communication with the cuttings discharge swivel 45 and cuttings/debris discharge hose 50 and an intake portion 55 in fluid communication with a source of the mortar-like substance and the body portion of the intake valve. As illustrated in FIG. 2, the intake portion 55 is preferably connected to the body of the intake valve at an angle α above a horizontal reference point, e.g., 90 degrees, to minimize back flow of the mortar-like substance into the cuttings/debris discharge hose 50. The angle a between intake portion 55 and body of the intake valve is preferably less than about 90 degrees, more preferably less than about 70 degrees, and most preferably less than about 50 degrees. The intake valve 53 also preferably has a valve (not shown) that can be manually or automatically closed to the source of the mortar-like substance during drilling. The intake valve 53 also preferably has a check valve (not shown), which can be manually or automatically activated, that prevents the mortar-like substance from entering the cuttings/debris discharge hose 50 when the mortar-like substance is pumped into return outlet 40 during support column formation.

[0017] It is also preferable to have a one-way check valve 60 at the one or more drilling fluid outlets communicating with the exterior annulus 35 near the drill bit 25. It is believed that some commercially available reverse circulation DTHs already provide such one-way check valves to prevent back flow of the cuttings/debris into the exterior annulus 35 during the drilling operation. Similar to its function during the drilling step, the one-way check valve 60 allows drilling fluid (e.g., gas, liquid, or mixture thereof) to exit the exterior annulus 35 while preventing back flow of the mortar-like substance into the drilling fluid exterior annulus 35. During the step of forming a column of mortar-like substance, it is preferred to provide a flow of drilling fluid at a rate sufficient to prevent back flow of the mortar-like substance. During the step of forming a column of mortar-like substance, the drilling fluid is pumped preferably at a pressure of less than 50 psi (345 kPa), more preferably at a pressure of less than 10 psi (70 kPa), and most preferably at a pressure of less than 5 psi (35 kPa). The mortar-like support column is completely formed when the DTH is completely removed from the drilled hole.

[0018] The present invention also includes a novel apparatus having a pipe casing 15 connected or attached to the down-the-hole hammer 20. In one embodiment, the pipe casing 15 can be connected to the back of the down-the-hole hammer, e.g., opposite the drill bit 25, thereby enveloping the drill string 37, as illustrated in FIGS. 1 and 2. In another embodiment, the pipe casing 15 can be connected to the down-the-hole hammer behind the drill bit 25 (not shown), e.g., attached to and enveloping at least a portion of the down-the-hole hammer, so that the pipe casing envelopes the down-the-hole hammer 20 and the drill string 3. In this embodiment, the pipe casing envelopes at least a portion, and preferably the entire length, of the down-the-hole hammer. In still another embodiment, the pipe casing 15 can be connected to the drill bit 25, thereby enveloping the down-the-hammer 20 and drill string 37. In the latter two embodiments, the drill bit 25 is preferably selected to have a diameter that is slightly larger than the down-the-hole hammer so that the size of the drill bit is substantially the same as the diameter of the pipe casing. The pipe casing can be connected by any method known in the art. For example, the pipe casing can be welded onto the down-the-hole hammer or connected using appropriate latches with rivets. These novel configurations allow the pipe casing to travel with the down-the-hole hammer without requiring a separate apparatus to drive or hammer the pipe casing into the hole behind the down-the-hole hammer. Furthermore, the connected pipe casing 15 helps to prevent cave in of the hole.

[0019] After complete removal of the DTH but before the mortar-like substance hardens or sets, the present method can further including inserting a reinforcing structure into the hole filled with the mortar-like substance. The reinforcing structure is typically made of metal but can be made of any suitable material that imparts strength to the support column. The reinforcing structure is selected from the group consisting of steel rods, steel piles, steel I-beams, steel cages, pipe, channel iron, and combinations thereof. The reinforcing structure is preferably a steel pile or a steel I beam. 

What is claimed is:
 1. A method for forming a support column in soil comprising: drilling a hole with a reverse circulation down-the-hole hammer apparatus having a down-the-hole hammer connected to a drill string with a return outlet; and forming a column of mortar-like substance by pumping a mortar-like substance down the return outlet while lifting the apparatus out of the hole.
 2. The method of claim 1, wherein the mortar-like substance is selected from the group consisting of grout, mortar, concrete, and mixtures thereof.
 3. The method of claim 2, wherein the mortar-like substance is concrete.
 4. The method of claim 1, wherein the lifting of the apparatus out of the hole is initiated about 30 seconds after the mortar-like substance is pumped into the return outlet.
 5. The method of claim 1, wherein the apparatus is lifted out of the hole at a vertical rate that is substantially equivalent to the vertical fill rate of the mortar-like substance into the portion of the hole evacuated by the apparatus.
 6. The method of claim 1, further comprising the step of installing a metal reinforcing structure into the hole filled with the mortar-like substance before it hardens.
 7. The method of claim 6, wherein the metal reinforcing structure is selected from the group consisting of steel rods, steel I-beams, steel cages, pipe, channel iron, and combinations thereof.
 8. The method of claim 7, wherein the metal reinforcing structure is a steel I-beam.
 9. The method of claim 1, wherein the apparatus further includes a pipe casing placed behind the down-the-hole hammer and enveloping the drill string.
 10. The method of claim 9, wherein the pipe casing is connected to the down-the-hole hammer.
 11. The method of claim 10, wherein the pipe casing is connected to the back of the down-the-hole hammer.
 12. The method of claim 10, wherein the pipe casing is connected to and envelopes at least a portion of the down-the-hole hammer.
 13. The method of claim 9, wherein the pipe casing is connected to the drill bit.
 14. An apparatus for drilling a hole in soil and forming a support column, the apparatus comprising, a down-the-hole hammer having a back end and a drill bit end; a drill string having an inner passageway, one end of the drill string connected to the back end of the down-the-hole hammer and the other end of the drill string connected to a cuttings discharge swivel; and a mortar-like substance intake valve attached to the cuttings discharge swivel.
 15. The apparatus of claim 14, wherein the intake valve comprises, a body portion in fluid communication with the cuttings discharge swivel at one end and a debris discharge hose at the other end, and an intake portion in fluid communication with a source of a mortar-like substance and the body portion of the intake valve.
 16. The apparatus of claim 15, wherein the intake portion of the intake valve is positioned to the body of the intake valve to form an angle that is less than about 90 degrees.
 17. The apparatus of claim 16, wherein the angle is less than about 70 degrees.
 18. The apparatus of claim 14 further comprising a pipe casing connected to the down-the-hole hammer and enveloping the drill string.
 19. The apparatus of claim 18, wherein the pipe casing is connected to the back of the down-the-hole hammer.
 20. The apparatus of claim 18, wherein the pipe casing is connected to and envelopes at least a portion of the down-the-hole hammer.
 21. The apparatus of claim 14, further comprising a pipe casing connected to the drill bit. 